C code for converting decimal to any base (from 2 to 36)

I have just recently started learning C. I wrote a very short program that converts between decimal and binary. I wanted to try and write a code that converts between decimal and any base (up until 36). However, my code just prints out garbage.

#include <stdio.h>
#include <string.h>

void printBase(int n, int k, int i, char a[])
{
    int placeholder;
    if (n != 0)
    {
        //return n % 2 + 10 * printBinary(n / 2);
        placeholder=(char)(n%k);
        if(placeholder>=10)
        {
            a[i] = (char)(placeholder - 10) + 'A';
        } else {
            a[i] = (char)placeholder;
        }
        i++;
        printBase(n/2, k, i, a);
    }
    for (i=0; a[i]!='\0'; i++)
    {
        printf("%c", a[i]);
    }
    return;
}

void reverse(char fromStr[], char toStr[])
{
    int i, j=0;
    i=getchar();
    for (i=0; fromStr[i]!='\0'; i++)
    {
        j++;
    }
    i=0;
    while (j>=0)
    {
        toStr[i]=fromStr[j];
        i++;
        j--;
    }
    printf("%s", toStr);
}

int main()
{
    int n, k;
    char a[81], b[81];
    setvbuf(stdout, NULL, _IONBF, 0);
    printf("Enter a deicmal number you want to convert to binary: ");
    scanf("%i", &n);
    fflush(stdout);
    printf("Enter a base: ");
    scanf("%i", &k);
    printBase(n, k, 0, a);
    //printf("%s", a);
    //reverse(a, b);
    return 0;
}

I thought the problem was with my reverse function but it works fine outside of this code. Even when I print out string a inside the printBase function it prints out garbage. What is the problem here?

Based on your code, the following does what you want. It places in a a reverse conversion that must still be printed backwards:

void convertBase(int n, int k, char a[])
{
    int j, i=0, sign= 0;
    if (n==0) a[i++]='0';
    if (n<0 ) {sign= -1; n= -n;}
    while (n>0) {
        j= n%k;
        if (j<10)
            a[i]= j+'0';
        else
            a[i]= j+'A';
        n= n/k;
        i++;
    }
    if (sign== -1) a[i++]= '-';
    a[i]= 0;
}

And here is revert:

void revStr(char *s)
{
    char c;
    int i=0, j=0;
    while (s[i]) i++; i--;
    while (i>j) {
        c= s[j];
        s[j]=s[i];
        s[i]= c;
        i--; j++;
    }
}